The present invention relates to a solid-state laser amplifying apparatus and a solid-state laser apparatus, capable of producing a high-power laser beam with a high quality under stable condition, and having a low-cost structure.
FIG. 1 is a side view for representing the structure of the conventional solid-state laser apparatus, or device as described in, e.g., the publication of "Solid-State Laser Engineering", Springer-Verlag, page 119 to 120. In this drawing, reference numeral 1 indicates a reflection mirror, reference numeral 2 shows a partial reflection mirror, reference numeral 3 represents a solid-state element containing an activated solid-state medium. As an example of a YAG laser, this solid-state element corresponds to Nd:YAG (Nd: Yttrium Aluminium Garnet) in which Nd is doped as the activated solid-state medium. Also, reference numeral 4 indicates an excitation light source, for example, a semiconductor laser in which GaAlAs is a major component. Reference numeral 5 denotes a power source for driving the excitation light source, reference numeral 6 shows a condenser lens, and reference numeral 7 is a laser beam produced in a laser resonator constructed by employing mirrors 1 and 2. Reference numeral 10 denotes such an optical thin film that the reflection mirror 1 total-reflects the laser beam 7 and total-transmits the laser beam of the semiconductor laser, reference numeral 40 indicates the laser light emitted from the semiconductor laser 4, reference numeral 70 indicates a laser beam externally derived from the partial reflection mirror 2, and reference numeral 100 shows a base.
The conventional solid-state laser apparatus is so constructed as explained above, in which the laser light of the semiconductor laser 4 energized by the power source 5 is conducted from the edge plane of the solid-state element 3 by the condenser lens 6, and is excited to be used as the laser amplifying medium. The natural emission light emitted from the laser amplifying medium is amplified while this natural emission light is reciprocated between the resonators arranged by the mirror 1 and the mirror 2, and then becomes the laser beam 7 with better directivity. When intensity of this laser beam 7 reaches a preselected value, this laser beam 7 is emitted as the laser beam 70 outside from the resonators.
In the above-described conventional solid-state laser apparatus, since it is so structured that the laser light of the semiconductor laser is conducted from the edge surface the solid-state element, the element portion near this edge surface is intensively excited. When the solid-state element is excited by such a high-power semiconductor laser in order to produce a high-power output, a light intensity distribution would be produced within the solid-state element, so that a beam shape would collapse. As a result, the high-power laser beam with high quality could not be produced.
Furthermore, in the conventional solid-state laser apparatus, since the absorption coefficient of the solid-state element depends upon the wavelength of the semiconductor laser, the wavelength of the semiconductor laser must be made coincident with the absorbing wavelength of the solid-state element in order to achieve a stable operation. FIG. 2 graphically represents a relationship between a wavelength of a semiconductor laser and an excitation efficiency when an Nd:YAG laser is employed as an example. To achieve such a stable operation that the excited oscillation efficiency is made constant, a semiconductor laser whose center wavelength is 810 nm is selected and a temperature thereof must be controlled. As a consequence, there are problems that the structure of the above-explained conventional solid-state laser apparatus becomes complex, the yield of manufacturing the semiconductor laser is lowered, and the manufacturing cost is increased, resulting in a high-cost solid-state laser apparatus.
Additionally, the conventional laser apparatus owns further problems. That is, since the laser apparatus is so arranged that the laser light of the semiconductor laser is condensed by the condenser lens onto one point of the solid-state element in order to be excited, when the beam projection direction of the semiconductor laser is varied due to mechanical vibrations, the location of the excitation unit is changed. Accordingly, a stable laser oscillation could not be established. Also, when one semiconductor laser is replaced by another semiconductor laser due to lifetime thereof, the replaced semiconductor laser must require fine positional/angular adjustments.